Patent GB-673749-A (GB)
Title: Improvements in or relating to velocity modulated electron discharge tubes
Inventor: LAMBERT DONOVAN ERNEST CHARLES
IPC: H01J25/08
Filed: 1949-03-23
Abstract: 673,749. Velocity-modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. March 23, 1949, No. 7895/49. Class 39 (i). [Also in Group XL (b)] An electron discharge device of the coaxial line electron velocity modulation type as described in Specification 587,664 having a metallic disc sealed to the envelope of the device and connected to the outer conductor of the internal coaxial line section, the said section having an electrical length an odd multiple of a quarter-wavelength at a given frequency in the operating band of the device and being connected at its open circuit end to a wave-guide having a cut-off frequency above any frequency in the said band, is characterized in that the other end of the said section is partially closed by a metallic member between the inner and outer conductors and that an extension of the inner conductor projects through the envelope of the said device, whereby the said device may be coupled to an external circuit such as a further coaxial line or a waveguide. In one embodiment, Fig. 1, the electron discharge device comprises a coaxial line resonator section mounted on a disc 7 which is sealed through the envelope 2. The outer wall 8 of the resonator forms the outer conductor of the coaxial line and the attenuating wave-guide 9 which prevents radiation from the lower end of the resonator. The resonator wall is slotted to allow passage of the electron beam from the gun 5, between plates 11 attached to the inner conductor 10, to the collector electrode 6, the slots being bounded by fins 12, aligned with the plates 11 to define gaps 13 and 14. The gun 5 and electrode 6 are mounted by support-rods (not shown) on base-pins 4. The upper end of the coaxial line section is partially closed by an inductive member 15, having three radial arms joining the inner and outer conductors, or alternatively two arms forming a diagonal strip across the coaxial line. An extension 16 of the inner conductor projects through the top of the envelope, to which it is sealed, and may be connected to the inner conductor of an external coaxial line, or may function as an antenna probe in a wave-guide. In an alternative arrangement, a capacitative coupling is obtained by replacing the member 15 by a disc mounted on conductor 10 and separated from the resonator wall by an annular gap. In a further embodiment, Fig. 4, also providing a capacitative coupling, the envelope 17 of the device is sealed at its upper end to the feathered flange 21 of an annular disc 18 which closely surrounds the inner conductor 19 of the quarter-wave line and is sealed thereto by a glass bead 20. The inner conductor 19 and its extension outside the envelope are integral, and energy is fed out of the oscillator by virtue of the annular aperture between the disc 18 and conductor 19. A conductor 24 shaped as a watch spring and serving as a high-frequency choke, provides a D.C. connection to the plates 11 which is necessary in the case of capacitative coupling to a waveguide. In an alternative arrangement similar to that of Fig. 4, a disc is connected to the inner conductor 19 and is separated from the annular disc, to which the envelope is sealed, by an annular aperture which is sealed with glass.